Jon,
Note the electrical section in the build manual (Chapter 25) as well as
the Rotax installation manual, brings alternator power to the panel
through a 25 amp switch/switch breaker.
Like you, I am not comfortable with that.
The "Cessna" style split master switch is a low amperage switch.
Normally, no more than 5 amps.
Here are the options.
Wire the C lead of the regulator to the alternator side of the split
master switch and continue the wire to a 5 amp breaker on the main bus.
When the switch is off, the control circuit input of the regulator is
cut and the regulator shuts down. (See the Aeroelectric Connection for
wiring techniques.) Now, Ducatti doesn't like this, as the circuit
diodes still have power coming in from the dynamo. Normally, you fly
with the alternator on all the time, so in a single alternator system,
no problem. If you want the alternator power off, it is probably an
emergency and who cares about the regulator then.
The alternative is to wire the alternator side of the split master
switch from a 2-3 amp circuit breaker to a 30 amp automotive relay
switch. The relay will keep you from having high amps coming to your
finger. I use this method a lot, especially with the dual alternator
setup. See
www.customflightcreations.com<http://www.customflightcreations.com/>
accessories/techniques section.
Notice that, the split master switch has a trick. Most of us want the
switch to be completely independent, that is, so one can select either
the alternator on or off and the master on or off completely
independent, but there is a small plastic tab that locks the two sides
together. So that both come on, but only one shuts off independently,
and the other shuts both off. I take a sharp Exacto knife and trim off
the small plastic locking tabs off and have mine completely independent.
Just a technique.
As for the diode, I have seen guys operate their planes for years
without it. However, it is a handy device. When the start switch is
disengaged, there is a slight chance that the field around the coil will
collapse and cause a reverse current called a fly back, and the diode
immediately neutralizes the fly back current. This allows the contactor
to separate cleanly and not do a quick open and close during the
disengage or hang-up which eventually will burn the start solenoid
contacts. It is an oldie but goodie that started in the late '50s when
the start solenoid and starter were in close proximity and field
shielding and wires were not as good as they are today. Our solenoid
has a really small coil and is well separated from other components so
the chance of a fly back is diminished, but not eliminated. Use the
diode and you should get a longer life out of your solenoid. Again,
reference an Aeroelectric Connection article
(http://www.matronics.com/aeroelectric/articles/spikecatcher.pdf<http://w
ww.matronics.com/aeroelectric/articles/spikecatcher.pdf>)
Use a ohm meter or a low power test light to get the diode direction if
you can't see the markings and figure out which way the power flows.
You can make your own hookups and put a 3/16 inch terminal on the ground
end of the diode and on the other end wire the diode end together with
the start wire into a spade female connector which connects to the
solenoid blade. Cover with heat shrink. Hook the 3/16 inch terminal to
the grounded base of the solenoid (grounded to the battery or negative
terminal of course). If you get it backwards, you'll know real quick.
You'll fry the diode and perhaps see some smoke. My friend Mike says
smoke is when the electric genie is released and the magic disappears.
Regards,
Bud Yerly
Europa Tech Assistance
Custom Flight Creations, Inc.
www.customflightcreations.com<http://www.customflightcreations.com/>
(813) 653-4989
----- Original Message -----
From: JonSmith<mailto:jonsmitheuropa@tiscali.co.uk>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Monday, January 17, 2011 2:25 PM
Subject: Europa-List: Electrical Question (Basic)
<jonsmitheuropa@tiscali.co.uk<mailto:jonsmitheuropa@tiscali.co.uk>>
Just a couple of basic questions (my electrics knowledge is very
basic)
I'm wiring up my new secondhand Rotax - upgrading my plane from a
previously installed car engine conversion. 95% of the aircraft wiring
aft of the firewall is common to both thank goodness but I have a
question about the alternator switch.
My panel currently has a combined double battery/ alternator switch
unit - one of the red coloured double rocker type switch units exactly
as found in Cessna 150's - in fact it has "Cessna" printed on the case.
My previous set up had a battery solenoid (still keeping that) but the
car-type alternator output was controlled by switching the field on/ off
via the alternator switch. Thus both switches had very low load through
them.
My limited understanding is that the Rotax does not have a separate
field like a conventional alternator and so the output from the
regulator must all go direct to the positive bus via the alternator
switch. My question is - can anyone advise if this Cessna switch is
man-enough for the job? - it has no rating markings on it and I can't
find it in any catalogues to check it's rating. (It looks pretty chunky
but size isn't everthing so to speak). Do other people use these or is
it best to have separate switch units?
Second quick question - the manual advises to connect a diode across
the starter solenoid coil. Do people bother to do this? If so, can
anyone advise a neat and easy way of physically connecting it. I have
one and can think of several ways of bodging it up but would much prefer
a professional looking solution.
Thanks in advance - any help appreciated! Jon
--------
G-TERN
Classic Mono
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